Tomaz Kastrun explains how to use rxInstallPackages to install packages on Microsoft R Server:
In rxInstallPackages function use computeContext parameter to set either to “Local” or to your “SqlServer” environment, you can also use scope as shared or private (difference is, if you install package as shared it can be used by different users across different databases, respectively for private). You can also specify owner if you are running this command out of db_owner role.
This updated installation method is certainly easier than the prior method, which included incantations and sacrificing a chicken.